The inquiry was prompted by a Dec. 1 derailment in the Bronx that killed four passengers and injured about 70 others. But it delves into a wide range of operations at the railroad, which serves New York and Connecticut.

In the days after the review began, the New York Times reported on an internal investigation that found workers padded time sheets and took trips to Pennsylvania for cigarettes and fireworks while they were on the clock.

The Metropolitan Transportation Authority, which operates Metro-North, has already made changes since the derailment, including appointing a new president, Joseph Giulietti, who replaced Howard Permut.

Days into the job, Giulietti released his 100-day plan for improvements, which includes including developing a new corporate safety policy.

He said the railroad is taking “aggressive actions” to assure that safety is its top priority.